1. Field of the Invention
This invention relates in general to apparatus for guiding a tape through one, or another, tape path in a tape recorder; more particularly, the invention is concerned with guides mounted in a coaxial-reel tape cassette, for guiding magnetic tape selectively through different tape paths, including one path which is so disposed in the tape recorder that a television signal train may be helically recorded on the tape. (As used herein, the term "recorder" shall be taken to mean apparatus which either plays back or records a video signal.)
2. Description Relative to the Prior Art
While not so restricted, the invention acquires a special significance when it is used to guide magnetic tape contained in a coaxial-reel cassette toward and away from a helical recording drum in a video tape recorder. Coaxial-reel cassettes are particularly well adapted for use with video recorders, which generally tend to be bulky, since cassette takeup and supply reels are rotated on the same axis. As is usual, coaxial-reel cassettes will have a pair of inclined or tapered guide posts which are so oriented as to take up the change in the tape level between the reels when the tape, fully contained in the cassette, passes directly from one reel to the other.
For helical recording, the tape is initially pulled from the cassette and wrapped around the recording drum at a helix angle. In addition, the helical recording format requires precise positioning of the span of tape which passes around the drum; positioning errors may cause, for example, mistracking during playback. Tracking problems are diminished, however, if the tape follows a precise path into, around, and out of the drum assembly. In one video recorder configuration, the paths into and out of the drum are horizontal and substantially in the same plane as the supply and takeup reels, respectively. The last post before the tape touches the drum and the first post after the tape leaves the drum are designed to change the tape's horizontal level a few degrees so as to dispose the tape properly to form a helix around the drum.
These factors suggest the use of the coaxial-reel cassette with the helical drum assembly; however, this combination is hampered significantly because the tape presented to the helical drum is last touched within the cassette by the inclined or tapered guide posts. What this means is that the last guide surfaces within the cassette will tend to force the tape into an inclined path which is not suitable for presentment to the drum assembly and its associated guides. On the other hand, the tape still needs to be positively guided to the vicinity of the drum at the correct height for proper helical scanning. In an attempt to meet this problem, copending U.S. patent application Ser. No. 606,995, in the name of Thomas G. Kirn, filed concurrently with and assigned to the same assignee as the present application, provides a rotatable guide, for use within a coaxial-reel cassette, having right circular conical and cylindrical surfaces on opposite sides thereof. By providing such a guide, with appropriate selective orientation, a tape may be translated directly between the reels by means of the conical surface, or guidedly directed to and from a recording drum, about which it helically wraps, by means of the cylindrical surface. Although the cylindrical surface will suitably direct the tape to the drum assembly, the upright conical surface still contributes undesirable stress differentials and distorts the tape as it passes thereabout from one coaxial level to the other.
Further refining this approach, copending U.S. patent application Ser. No. 607,002, in the name of Douglass L. Blanding, filed concurrently with and assigned to the same assignee as the present application, provides a guide for use within a coaxial-reel cassette, having composite conical and cylindrical surfaces. By obliquely orienting the conical surface with respect to the cylindrical surface, their composite juncture presents a smooth, continuous guiding surface. Such a guide translates the tape free of distortion directly between the reels by means of the cylindrical and conical surfaces together, or guidedly directs the tape to or from the recording drum, about which it helically wraps, by means of the cylindrical surface alone. When the latter path is so directed to the drum that the tape cannot clear the conical surface, the post is rotated sufficiently to provide such clearance.
Apart from the selective use of two contiguous guiding surfaces mounted within a cassette, it is known to selectively substitute a guide post mounted on the recorder for a post located in the cassette so as to achieve selective guiding through two tape paths, e.g., U.S. Pat. No. 3,678,213. In such a substitution, a spring-biased post, located in a coaxial-reel cassette, is forced out of the tape path by a fixed post on the recorder deck when the cassette is emplaced on the recorder; therefore, two different guide posts are provided for two different paths. However, high speed winding with the tape contained in the cassette is hindered by the presence of the incorrect guide surface. Belgian Patent No. 534,063 illustrates another form of substitution, although not adapted to a cassette, in which a capstan protrudes through an angular slot in a rotatable plate mounted on a recorder. A pressure roller and a guide roll are so mounted on the plate relative to the slot that the plate may be rotated between two tape-encountering positions. In the first position, the tape is pressed against the capstan by the pressure roller to drive the tape. In the second position, with the plate rotated sufficiently that the pressure roller releases the tape from the capstan, the guide roll holds the tape away from the capstan to enable the rewinding of the tape.
Turning now to another course of development in the prior art, U.S. Pat. No. 3,790,055 (to Sims) discloses the cooperation of a capstan with a post in a cassette for quickly stopping the motion of a magnetic tape. The post, which Sims describes as a motion control device, consists of an elongated member having a central cavity within which a freely rotatable capstan fits. The member rotates from a driving position exposing the enclosed capstan to the tape through a cut-away sidewall to a braking position wherein the tape is separated from the capstan and pinched between the sidewall of the member and a resilient pressure member. A similar type of motion control device had previously been proposed in U.S. Pat. No. 2,590,665, although not in conjunction with a tape cassette. For purposes that later will become clearer, the Sims patent is of interest merely because it shows a situation in which a capstan may cooperate with a rotatable element in a cassette.